What causes pityriasis rosea?

Experts aren't sure what causes pityriasis rosea. Unlike many other skin conditions, it is not an
allergic reaction or caused by a
fungus or bacteria. It may be caused by a virus.

The rash does not appear to spread from person to person.

What are the symptoms?

Pityriasis rosea causes a
rash.

The rash often begins with a single, round or
oval, pink patch that is scaly with a raised border (herald patch). The size of
the patch ranges from
2 cm (0.8 in.) to
10 cm (3.9 in.). The larger
patches are more common. See a picture of a
herald patch.

Days to weeks later, salmon-colored,
1 cm (0.4 in.) to
2 cm (0.8 in.) oval patches
appear in batches on the abdomen, chest, back, arms, and legs. Patches
sometimes spread to the neck but rarely to the face.

Patches on the
back are often vertical and angled to form a "Christmas tree" or "fir tree"
appearance.

Mild itching is a problem for about half of the people who get the rash.

The rash usually lasts 6 to 8
weeks, but it can last up to several months.

In rare cases, the rash may take other forms. Rounded bumps (papular rash)
may be seen in young children, pregnant women, and people who have dark skin.
Blisters (vesicular rash) may be seen in infants and young children. In some
people, the herald patch may not appear, or two herald patches may appear close
together.

Before the herald patch appears, you may feel tired and
as though you have a cold. You may have a headache, nausea, sore throat, and
loss of appetite.

A rash similar to pityriasis
rosea also can be caused by
syphilis and by certain medicines such as
antibiotics.

If you get a rash on the palms of your hands or the soles of your feet, see your doctor. This can be a sign of something more serious than pityriasis rosea.

How is pityriasis rosea diagnosed?

Your doctor
will diagnose pityriasis rosea by looking at the rash. Diagnosis can be
hard when only the herald patch is visible, because the condition is often
mistaken for ringworm or eczema at this time. After the rash appears, diagnosis
is generally clear.

If the diagnosis is unclear, your doctor may
do a
potassium hydroxide (KOH) test to make sure the rash
is not caused by a
fungal infection. A skin sample may be taken from the
infected area and examined under the microscope (biopsy). If the
diagnosis is unclear in a sexually active person, a test for syphilis is often
done.

How is it treated?

Pityriasis rosea goes away without treatment. It usually lasts about 6 to 8 weeks. If the rash itches, you may wish to use skin lotions and lubricants to soothe itching. If symptoms are severe, your doctor may prescribe anti-inflammatory medicines such as corticosteroids to relieve itching and reduce the rash.

Although treatment isn't needed, antiviral medicines like acyclovir may shorten the time you have the rash, especially if you take them when the rash first starts.

Exposing
the rash to sunlight may make it go away more quickly. But exposing your skin
to the sun too long can result in sunburn and increase your risk of
skin cancer.

If the rash lasts more than
3 months, contact your doctor.

To relieve itching at home:

Try to stay cool. Getting too warm and sweaty can make the rash and itching worse.

Avoid taking hot showers or baths. Keep the water as cool as
you can tolerate.

Try an oatmeal bath, such as Aveeno Colloidal
Oatmeal bath, to help relieve itching. You may also wrap
1 cup of oatmeal in a cotton cloth and boil as
you would to cook oatmeal. Use this as a sponge and bathe in cool water without
soap.

Try an
over-the-counter 1% hydrocortisone cream for small
itchy areas. Use the cream very sparingly on the face or genitals.
Note: Do not use the cream on children younger than age
2 unless your doctor tells you to. Do not use in the rectal or vaginal area in
children younger than age 12 unless your doctor tells you to.